1. Field of Invention
This invention provides a method for determining the effect of a chemical compound on a given microorganism, subsequently called the analytic chemostat method.
2. Description of Prior Art
Determining the effect of chemical compounds on microbial cultures is of importance both in clinical applications end in assessing new compounds for antimicrobial activity. Although a number of assays have been developed for this purpose none has achieved a high degree of precision and reproducibility This may be because all the methods currently in use involve inoculating the organism to be tested into a fixed quantity of media, solid or liquid. Organisms growing in this manner undergo a succession of physiological states caused by the depletion of nutrients and the build up of toxic metabolites. Indeed, cultures grown on limited media will eventually stop growing independently of the action of the introduced compound. The effect of the antimicrobial agent is therefore combined with a number of naturally occuring inhibitory factors, complicating interpretation of the results.
In order to determine the effect of an antimicrobial agent on microorganisms growing in culture it is necessary to have some method of measuring growth or metabolic activity and to measure growth in the presence, and in the absence, of the compound tested. If the cultures are to be grown on limited media two cultures are required, with growth in the absence of the antimicrobial agent serving as the control experiment. Growth is traditionally determined by visually inspecting the media for colonies, in the case of solid media, or opacity in liquid media, after a period of incubation. This is essentially an "all or nothing" approach and organisms are regarded as sensitive, or resistant, to a particular concentration of an antimicrobial compound. To achieve greater precision several cultures are inoculated simultaneously, with the concentration of antimicrobial agent varied by a series of dilutions. Using these methods the minimum concentration needed to inhibit growth, or MIC, can be determined within approximately a factor of two. The advent of more sophisticated methods of measuring growth has done little to improve on these results.